Some of the documentation for QEMU "tools" which are standalone
binaries like qemu-img is an awkward fit in our current 5-manual
split. We've put it into "interop", but they're not really
about interoperability.

Create a new top level manual "tools" which will be a better
home for this documentation. This commit creates an empty
initial manual; we will move the relevant documentation
files in a subsequent commit.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20200217155415.30949-2-peter.maydell@linaro.org